This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
In the use of the tlake or natural spawn, the planting is accomplished in a similar way, but larger pieces of the spawn are used, two or three times the size of the pieces of brick employed. Some use a large handful. In some few cases, the growers use a flake spawn from their own crop. That is, each year a few beds are spawned from material which has been kept over from the previous season. This is often kept in boxes, in cool places, where it does not thoroughly dry out. In this way, the spawn is used over and over again, until it becomes much less vigorous than natural spawn, or a spawn which is only one or only a few generations distant from the natural spawn. This is seen in the less certainty with which the spawn runs through the bed, in the smaller crop of mushrooms, and their gradual deterioration in size. Some few practice the method of breaking down the bed after the crop has been nearly gathered, using this weak spawn to inoculate fresh beds. This practice is objectionable for the same reason that long cultivated spawn is objectionable.
After the beds have been planted with the spawn, the next thing is to soil them. That is, the manure in the bed is covered with a layer of loam soil, or garden soil, to the depth of two inches, then spread evenly over the bed, leveled off, and tamped down, though not packed too hard, and the surface is smoothed off. The time at which the soiling is done, varies also with different operators. Some soil immediately after planting the spawn. Others believe that the spawn will most certainly fail to run if the beds are soiled immediately after planting. These operators wait two or three weeks after the spawn has been planted to soil it. Others wait until the temperature of the bed has fallen from 8o° or 850 at the time of spawning, to 70° or 6o° F. Soiling at this temperature, that is, at 6o° or 70° F., probably prevents the rapid cooling down of the bed, and it is desirable to soil, at least at this temperature, for that purpose. When the beds are soiled, they are then left until the crop is ready to gather. Some operators give no further attention to the beds after soiling, other than to water the beds, if that becomes necessary. It is desirable to avoid watering, if the bed can be kept at the right state of moisture without. In watering the beds while the spawn is running, there is danger of killing the young spawn with the water. Wherever it is necessary, however, if the material in the bed becomes too dry, lukewarm water should be used, and it should be applied through a fine rose of a watering pot.
While some operators after soiling the bed give no further care to it until the bed is bearing, others cover the beds with some litter, in the form of straw or excelsior. This is done for the purpose of conserving the moisture in the bed, and especially the moisture on the surface of the bed. Sometimes where there is a tendency for the material in the bed to become too dry, this litter on the surface retards the loss of moisture. Also, the litter itself may be moistened and the bed can absorb some moisture in this way, if it is desirable to increase the moisture content of the bed slightly.
When the spawn has once run well through the bed, watering can be accomplished with less danger of injury, yet great care must be used even now. The spawn will run through a bed with a somewhat less moisture content in the material than is necessary for drawing off the crop of mushrooms, though, of course, the spawn will not run if the bed is too dry. The only way to see if the spawn has run satisfactorily is to open up the bed at one or two points to examine the material, opening it up slightly. If the spawn has run well, a very delicate white "fiber," the mycelium, can be seen penetrating all through the material. This handful can be replaced in the bed, packed down, and the soil covered over and firmed again at this point.
When the mushrooms begin to appear, if the bed is a little dry, it should be watered from time to time through the fine rose of a watering pot. Lukewarm water should be used. Nearly all growers water the beds during the picking of the crop, or during the period of gathering the crop. At the first few waterings, water should not be sprinkled on the beds to wet them entirely through. Enough water is applied to diffuse a short distance only through the upper surface of the bed. At the next watering, several days later, the moisture is carried further down in the bed, and so on, through the several weeks, or months, over which the harvesting season extends. The object of thus gradually moistening the bed from above, is to draw the crop from the spawn at the surface of the bed first, and then, as the moisture extends downward, to gradually bring on the crop from the "fiber" below.